1. Field of the Invention
The present invention relates to an image projection apparatus, a memory control apparatus, a laser projector, and a memory access method.
2. Description of the Related Art
Currently, there is developed an image projection apparatus using a laser as a light source (hereinafter also referred to as a “projector”). The use of a laser as a light source enables a projector to attain extremely high chroma and high color reproduction. A DLP (Digital Light Processing) method, a LCOS (Liquid Crystal On Silicon) method, and a method using an MEMS (Micro-Electro-Mechanical-System) are known as methods for projecting a laser to a surface.
However, in a case where a laser is projected from a projector, it is known that a projection image projected by the projector is distorted and shaped as a trapezoid when the angle formed by projection image and a light beam at the center of the projected laser is not perpendicular (hereinafter also referred to as “oblique projection”).
FIGS. 38A-38C are schematic diagrams for describing a projection image in a case where oblique projection occurs in an optical system. FIG. 38A illustrates an example of a projection image in a case of no oblique projection. FIG. 38B illustrates an example of a projection image in a case of oblique projection (upward projection). FIG. 38C illustrates another example of a projection image in a case of oblique projection (downward projection).
In FIG. 38A, the projection image is projected without any distortion because the light from the projector is projected at a distance (distance from the projector to the wall) and an angle (angle formed by the projection image and the light beam at the center of the projected light) that are anticipated at the time of designing the optical system. In FIG. 38B, an upper side of the projection image is longer than a lower side of the projection image because the light projected from the projector is inclined upward with respect to the angle anticipated at the time of designing the optical system. As a result, the projection image is distorted and becomes a trapezoid shape.
In FIG. 38C, a lower side of the projection image is longer than an upper side of the projection image because the light projected from the projector is inclined downward with respect to the angle anticipated at the time of designing the optical system. As a result, the projection image is distorted and becomes a trapezoid shape.
Although there are several methods for correcting a distorted projection image from a trapezoid shape to a quadrate shape, projectors such as a projector using a DLP process (DLP projector) or a projector using a LCOS process (LCOS projector) needs to perform an image process on an input image (image to be input to an optical polarization element) beforehand. That is, the DLP projector and the LCOS are required to perform an image process (e.g., pixel skipping, pixel interpolation) on the input image beforehand because a single pixel formed on optical polarization element corresponds to a single pixel of an image formed on a projection plane.
FIG. 39A is a schematic diagram for describing the DLP projector. The DLP projector uses a DMD (Digital Micromirror Device) having mirrors integrated in units of pixels. FIG. 39A illustrates an example of a DMD corresponding to 4 pixels (2×2). In the DMD of FIG. 39A, the upper right mirror is switched off whereas the other mirrors are switched on. Accordingly, in the projection image projected from the light source, a black image is formed on the upper right pixel in correspondence with the status of the mirrors of the DMD. Hence, with a DLP projector, 1 mirror of a polarization element corresponds to 1 pixel of a projection image.
FIG. 39B is a schematic diagram for describing correction of a trapezoid image in a case of using a DLP projector. Because a micro-mirror of a DLP (as well as a liquid crystal of a LCOS projector) has a one-to-one relationship with respect to a pixel of a projection image, the projector cannot change the position of a pixel being projected. For example, in order to correct a distorted projection image as illustrated on the left side of FIG. 3B to a rectangle as illustrated on the right side of FIG. 3B, it is necessary to reflect light from the micro-mirrors corresponding to the pixels of the rectangle. This results in reduction of valid pixels. Further, degradation of the projection image may occur due to pixels of the original image data being skipped in association with the reduction of valid pixels.
FIG. 40A is a schematic diagram for describing a projector using a laser scanning method (laser scanning type projector). The laser scanning type projector forms an image on a projection plane by polarizing a laser with a 2D (two-dimensional) scanner (x-y scanner). In FIG. 40A, the laser radiated from a laser oscillator transmits through a half-mirror. Then, the laser is polarized by the 2D scanner. Then, the path of the laser is changed by the half-mirror, to thereby form an image on a screen. Because the 2D scanner is continuously operated, an area to be depicted can be adjusted by adjusting the timing of radiating the laser. Thereby, an area equal to or smaller than a single pixel can be depicted.
FIG. 40B is a schematic diagram for describing trapezoid correction of a laser scanning type projector. With a laser scanning type projector, trapezoid correction can be achieved without reduction of valid pixels by making slight adjustments of pixel positions by adjusting the timing of radiating a laser.
However, as disclosed in Japanese Laid-Open Patent Publication No. 2007-199251, controlling the oscillation of an oscillation mirror based on the position of a vertical axis is difficult and unrealistic considering that the oscillation mirror is oscillating in a resonant state.
Further, in Japanese Laid-Open Patent Publication No. 2004-295029 where the timing of radiating a laser is controlled, the trajectory of the laser formed by an oscillation mirror in a resonant state is calculated with actual numbers including trigonometric functions and inverse trigonometric functions. Therefore, in a case of correcting the timing of radiating the laser while calculating a depiction area of the laser at real time, there is a problem in which the calculation cannot keep up with the correction.
Further, in Japanese Laid-Open Patent Publication No. 2010-230730, the method for calculating non-depiction areas or controlling the laser after the calculation are not described in detail. Therefore, it is assumed that the technology disclosed in Japanese Laid-Open Patent Publication No. 2010-230730 contains problems yet to be resolved in order to be realized.